2) Bring the milk to a boil in a medium saucepan and slowly pour the hot milk into the chocolate mixture. Combine well, then pour the mixture back into the pan.
3) Cook the mixture over a low heat, stirring constantly with a whisk or wooden spoon, until thickened. If the mixture begins to curdle, remove it from the heat and beat it vigorously with a wire whisk.
4) Remove the pan from the heat, add the chocolate, butter, vanilla and double cream, and mix until the chocolate and butter are melted.
5) Pour into serving bowls. Place cling film directly on top of the pudding, and chill thoroughly. Remove the cling film before serving.